The present invention relates to a rendering processor for generating data to be displayed on a display device of a display control apparatus, such as a CRT display, and in particular, to a hardware system for generating images and three-dimensional data at a high speed. The present invention further relates to an apparatus which displays on a display an image with gradation generated by the rendering processor, and in particular, to an apparatus for displaying on a display images having different lightness or luminance levels for the respective pixels associated with influence from illuminated light and the like.
Conventionally, for apparatuses to effect a display control, particularly to execute drawing processing, there have been proposed many processing systems.
For example, the Japanese Patent Unexamined Publication No. 59-229669 describes an example of processing to rotate an image in which coordinate values of a destination image are obtained corresponding to coordinates of lattice points of a source image. In this method, there does not appear any trouble if a DDA circuit for a line expansion is provided only for the (X, Y) coordinates of the destination; however, there actually exists problems that the processing performance is determined depending on the size of an image on the source side and that images of different lattice points are written or are not written at a destination lattice point many times in some cases.
The Japanese Patent Examined Publication No. 57-57715 describes a method in which gradation of each pixel is attained in a triangle for which a gradation value is beforehand assigned to a vertex of the triangle. According to this method, a shading operation on a graphic image is accomplished by a hardware system; however, since a memory access is necessary for each generation of a pixel, particularly, in the shading operation to generate pixels in a direction parallel to the raster, there arises a problem related to the processing performance.
The Japanese Patent Unexamined Publication No. 60-252394 discloses a patent related to a color image display apparatus, and particularly, to a color image display apparatus including a variable configuration of memory planes. In this method, the bus configuration with respect to the CPU can be kept unchanged regardless of the number of memory planes; however, there is not provided an independent arithmetic circuit for each memory plane, which leads to a problem of performance associated with operations, for example, for the image processing.
The prior art technologies above aim at a high-speed processing for a partial processing of the graphic or image processing, namely, the inventions are to be implemented only either in the graphic processing or the image processing.
However, since sophisticated or developed functions, a higher precision, and an expansion of the display screen are desired in the screen display operation, it is necessary to satisfy the requirements above and at the same time to reduce the response time for the screen display operation.
Furthermore, in order to effect a high-speed processing of a color image, there has been disclosed, for example, "an apparatus for accessing an image memory" in the Japanese Patent Application No. 59-30278 in which an arithmetic unit is disposed for each plane of the frame memory so as to effect a concurrent processing. However, in this prior art technology, a comprehensive arithmetic system sufficiently processing an image with gradation has not been considered; consequently, if it is desired to execute a gradation change processing to alter gradation of an image, the host processor (CPU) is required to achieve again a computation of the image, which leads to a problem that the real time change of the display cannot be carried out.
Next, referring to drawings, a detailed description will be given of requirements of application to clarify the problem above.
As shown in FIG. 27, image data A on the left-hand side is defined with gradation in a two-dimensional plane. When the image data A is subjected to a texture mapping processing to apply the image data A on the entire surfaces of a rectangular parallel-piped as shown on the right-hand side so as to configure an image B, an image like an actual scene cannot be attained unless the mapping (image conversion or transform) is accomplished so as to develop a gradation difference between the rear side and the front side of the plane (or between the deeper side and the near side viewed from the side of the eyes of the user). Consequently, a higher density is assigned to the front side and a lower density is assigned to the rear side.
To implement this processing, for example, for pixels to be mapped onto the rear side, the value of each pixel of the gradation image on the two-dimensional plane are multiplied by 0.6 for the mapping operation; whereas for pixels to be mapped onto the front side, the value of each pixel of the gradation image on the two-dimensional plane are multiplied by 1.0 for the mapping operation; moreover, each pixel between the rear and front sides are required to be multiplied by (0.6-1.0) so as to take an intermediate value. As a result, the density of the portion of the image on the rear side becomes thinner than the original density thereof on the two-dimensional plane.
The density conversion in this processing is achieved by a host processor and hence a real time processing of the density conversion cannot be easily accomplished.